Living in the Matrix with Bytecode Manipulation

Transcription

1 Living in the Matrix with Bytecode Manipulation QCon NY 2014

2 Ashley Puls Senior Software Engineer New Relic, Inc.

3 Follow Along

4 Outline What is bytecode? Why manipulate bytecode? What frameworks can be used to manipulate bytecode? Examine two frameworks in depth

5 What is Java bytecode?.java file Java compiler (javac).class file Java Virtual Machine Native OS Java Runtime System Bytecode Verifier Class Loader Source:

6 What is Java bytecode?.java file Java compiler (javac).class file Java Virtual Machine Native OS Java Runtime System Bytecode Verifier Class Loader Source:

7 What is Java bytecode? Instruction set of the Java Virtual Machine.java file Java compiler (javac).class file Java Virtual Machine Native OS Java Runtime System Bytecode Verifier Class Loader Source:

8 Why learn about Java bytecode manipulation frameworks?

9 Why learn about Java bytecode manipulation frameworks? A bytecode manipulation framework is likely already on your stack Spring Hibernate Groovy Clojure Eclipse JRuby

10 Why learn about Java bytecode manipulation frameworks? A bytecode manipulation framework is likely already on your stack Spring Hibernate Groovy Clojure Eclipse JRuby Its really fun!!!

11 Why learn about Java bytecode manipulation frameworks? program analysis find bugs in code examine code complexity generate classes proxies remove access to certain APIs compiler for another language like Scala transform classes without Java source code profilers optimization and obfuscation additional logging

12 Why learn about Java bytecode manipulation frameworks? program analysis find bugs in code examine code complexity generate classes proxies remove access to certain APIs compiler for another language like Scala transform classes without Java source code profilers optimization and obfuscation additional logging

13 Logging Source:

14 Logging Source:

15 Logging Source:

16 Logging Audit Log: a message should be logged every time an important method is called Source:

17 Logging Audit Log: a message should be logged every time an important method is called log important input parameters to the method Source:

18 Logging public class BankTransactions { public static void main(string[] args) { BankTransactions bank = new BankTransactions(); // login and add i dollars to account for (int i = 0; i < 100; i++) { String accountid = "account" + i; bank.login("password", accountid, "Ashley"); bank.unimportantprocessing(accountid); bank.finalizetransaction(accountid, Double.valueOf(i)); System.out.println( Transactions completed );

19 Logging public class BankTransactions { public static void main(string[] args) { BankTransactions bank = new BankTransactions(); // login and add i dollars to each account for (int i = 0; i < 100; i++) { String accountid = "account" + i; bank.login("password", accountid, "Ashley"); bank.unimportantprocessing(accountid); bank.finalizetransaction(accountid, Double.valueOf(i)); System.out.println( Transactions completed );

20 Logging /** * A method annotation which should be used to indicate important methods whose * invocations should be logged. * */ ImportantLog { /** * The method parameter indexes whose values should be logged. For example, * if we have the method hello(int parama, int paramb, int paramc), and we * wanted to log the values of parama and paramc, then fields would be ["0", * "2"]. If we only want to log the value of paramb, then fields would be * ["1"]. */ String[] fields();

21 Logging public void login(string password, String accountid, String username) { // login logic public void finalizetransaction(string accountid, Double moneytoadd) { // transaction logic

22 = { "1", "2" ) public void login(string password, String accountid, String username) { // login = { "0", "1" ) public void finalizetransaction(string accountid, Double moneytoadd) { // transaction logic

23 = { "1", "2" ) public void login(string password, String accountid, String username) { // login logic A call was made to method "login" on class "com/example/qcon/mains/banktransactions". Important params: Index 1 value: ${accountid Index 2 value: = { "0", "1" ) public void finalizetransaction(string accountid, Double moneytoadd) { // transaction logic

24 = { "1", "2" ) public void login(string password, String accountid, String username) { // login logic A call was made to method "login" on class "com/example/qcon/mains/banktransactions". Important params: Index 1 value: ${accountid Index 2 value: = { "0", "1" ) public void finalizetransaction(string accountid, Double moneytoadd) { // transaction logic A call was made to method "finalizetransaction" on class "com/example/qcon/ mains/banktransactions". Important params: Index 0 value: ${accountid Index 1 value: ${moneytoadd

25 Java Agent Ability to modify the bytecode without modifying the application source code Added in Java 1.5 Docs: java/lang/instrument/package-summary.html

26 Typical Java Process java com/example/qcon/mains/banktransactions JVM Classloader BankTransactions.class public static void main(string[] args) Transactions completed

27 Java Agent java -javaagent:/path/to/agent.jar com/example/qcon/mains/ BankTransactions Agent JVM

28 Java Agent java -javaagent:/path/to/agent.jar com/example/qcon/mains/ BankTransactions JVM

29 Java Agent java -javaagent:/path/to/agent.jar com/example/qcon/mains/ BankTransactions Agent JVM

30 Java Agent java -javaagent:/path/to/agent.jar com/example/qcon/mains/ BankTransactions Agent Agent.class void premain(string agentargs, Instrumentation inst) JVM 1. call Agent premain in manifest 2. JVM registers my transformer MyTransformer.class byte[] transform(..., byte[] banktransbytes)

31 Java Agent java -javaagent:/path/to/agent.jar com/example/qcon/mains/ BankTransactions Agent Agent.class void premain(string agentargs, Instrumentation inst) MyTransformer.class byte[] transform(..., byte[] banktransbytes) JVM 1. call Agent premain in manifest 2. JVM registers my transformer 3. Give BankTransactions bytes to MyTransformer 4. MyTransformer provides bytes to load

32 Java Agent java -javaagent:/path/to/agent.jar com/example/qcon/mains/ BankTransactions Agent Agent.class void premain(string agentargs, Instrumentation inst) MyTransformer.class byte[] transform(..., byte[] banktransbytes) JVM 1. call Agent premain in manifest 2. JVM registers my transformer 3. Give BankTransactions bytes to MyTransformer 4. MyTransformer provides bytes to load BankTransactions.class void main(string[] args) 5. BankTransactions loaded and main runs Transactions completed

33 lets code Manifest: Premain-Class: com.example.qcon.agent.agent

34 lets code Manifest: Premain-Class: com.example.qcon.agent.agent package com.example.qcon.agent; public class Agent { public static void premain(string agentargs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addtransformer(new ImportantLogClassTransformer());

35 lets code Manifest: Premain-Class: com.example.qcon.agent.agent package com.example.qcon.agent; public class Agent { public static void premain(string agentargs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addtransformer(new ImportantLogClassTransformer());

36 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { //TODO return null;

37 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { //TODO return null;

38 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { System.out.println(" Loading class: " + classname); return null;

39 lets code Starting the agent Loading class: java/lang/invoke/methodhandleimpl Loading class: java/lang/invoke/membername$factory Loading class: java/lang/invoke/lambdaform$namedfunction Loading class: java/lang/invoke/methodtype$concurrentweakinternset Loading class: java/lang/invoke/methodhandlestatics Loading class: java/lang/invoke/methodhandlestatics$1 Loading class: java/lang/invoke/methodtypeform Loading class: java/lang/invoke/invokers Loading class: java/lang/invoke/methodtype$concurrentweakinternset$weakentry Loading class: java/lang/void Loading class: java/lang/illegalaccessexception Loading class: sun/misc/postvminithook Loading class: sun/launcher/launcherhelper Loading class: java/util/concurrent/concurrenthashmap$forwardingnode Loading class: sun/misc/urlclasspath$fileloader$1 Loading class: com/example/qcon/mains/banktransactions Loading class: sun/launcher/launcherhelper$fxhelper

40 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { System.out.println(" Loading class: " + classname); return null;

41 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { // manipulate the bytes here and then return them return null;

42 Bytecode Manipulation Frameworks ASM: BCEL: CGLib: Javassist: Serp: Cojen: Soot:

43 Bytecode Manipulation Frameworks ASM: BCEL: CGLib: Javassist: Serp: Cojen: Soot:

44 Javassist Java Programming Assistant Subproject of JBoss Actively updated Version released May 2014 Source code: javassist Documentation: ~chiba/javassist/tutorial/tutorial.html

45 Javassist CtClass: represents a compile time class ArrayList HashMap

46 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ArrayList HashMap

47 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ArrayList ArrayList HashMap HashMap

48 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ArrayList ArrayList HashMap HashMap BankTrans

49 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass ArrayList ArrayList HashMap HashMap BankTrans

50 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath( BankTrans, classbytes); ArrayList ArrayList HashMap HashMap BankTrans

51 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath( BankTrans, classbytes); ArrayList ArrayList HashMap HashMap BankTrans BankTrans

52 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath( BankTrans, classbytes); CtClass bank = Classpool.getDefault().get( BankTrans ); ArrayList ArrayList HashMap HashMap BankTrans BankTrans

53 Javassist CtClass: represents a compile time class ClassPool: container of CtClass objects ByteArrayClassPath: converts a byte[] to a CtClass Classpool.getDefault().insertClassPath(new ByteArrayClassPath( BankTrans, classbytes); CtClass bank = Classpool.getDefault().get( BankTrans ); ArrayList ArrayList HashMap HashMap BankTrans BankTrans BankTrans

54 Javassist CtClass: represents a compile time class BankTrans

55 Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor BankTrans init

56 Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor CtMethod: represents a compile time class BankTrans init login process

57 Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor CtMethod: represents a compile time method CtMethod loginmethod = loginctclass.getdeclaredmethod( login ); BankTrans init login process

58 Javassist CtClass: represents a compile time class CtConstructor: represents a compile time constructor CtMethod: represents a compile time method CtMethod loginmethod = loginctclass.getdeclaredmethod( login ); BankTrans init login process login

59 Javassist CtMethod: represents a compile time method login

60 Javassist CtMethod: represents a compile time method Modifications: login

61 Javassist CtMethod: represents a compile time method Modifications: putmethod.insertbefore( System.out.println(\ before method\ ); ); putmethod.insertafter( System.out.println(\ after method\ ); ); login

62 Javassist CtMethod: represents a compile time method Modifications: putmethod.insertbefore( System.out.println(\ before method\ ); ); putmethod.insertafter( System.out.println(\ after method\ ); ); login System.out.println( before method ); System.out.println( after method );

63 Javassist CtMethod: represents a compile time method Modifications: CtClass exceptiontype = classpool.get( java.io.ioexception ); putmethod.addcatch( {System.out.println($e); throw $e, exceptiontype); login

64 Javassist CtMethod: represents a compile time method Modifications: CtClass exceptiontype = classpool.get( java.io.ioexception ); putmethod.addcatch( {System.out.println($e); throw $e, exceptiontype); login System.out.println( exception ); throw exception;

65 Javassist CtMethod: represents a compile time method Modifications: putmethod.insertat(5, true, System.out.println(\ hello\ ); ); login

66 Javassist CtMethod: represents a compile time method Modifications: putmethod.insertat(5, true, System.out.println(\ hello\ ); ); login System.out.println( hello );

67 Javassist CtMethod: represents a compile time method Modifications: insertbefore insertafter insertat addcatch login System.out.println( before method ); System.out.println( hello ); System.out.println( exception ); throw exception; System.out.println( after method );

68 Javassist CtMethod: represents a compile time method Modifications: insertbefore insertafter insertat addcatch Freeze Class: login System.out.println( before method ); System.out.println( hello ); System.out.println( exception ); throw exception; System.out.println( after method );

69 Javassist CtMethod: represents a compile time method Modifications: insertbefore insertafter insertat addcatch Freeze Class: writefile() toclass() tobytecode() login System.out.println( before method ); System.out.println( hello ); System.out.println( exception ); throw exception; System.out.println( after method );

70 lets code

71 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { //TODO return null;

72 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { //TODO return null;

73 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { 1. convert byte array to a ct class object 2. check each method of ct class for 3. annotation present on method, then a. get important method parameter indexes b. add logging statement to beginning of the method return null;

74 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); 2. check each method of ct class for 3. annotation present on method, then a. get important method parameter indexes b. add logging statement to beginning of the method return null;

75 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); 3. annotation present on method, then a. get important method parameter indexes b. add logging statement to beginning of the method return null;

76 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); if (annotation!= null) { List<String> parameterindexes = getparamindexes(annotation); return null; b. add logging statement to beginning of the method

77 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); if (annotation!= null) { List<String> parameterindexes = getparamindexes(annotation); currentmethod.insertbefore(createjavastring( currentmethod, classname, parameterindexes)); return cclass.tobytecode(); return null;

78 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); if (annotation!= null) { List<String> parameterindexes = getparamindexes(annotation); currentmethod.insertbefore(createjavastring( currentmethod, classname, parameterindexes)); return cclass.tobytecode(); return null;

79 lets code private Annotation getannotation(ctmethod method) { MethodInfo minfo = method.getmethodinfo(); // the attribute we are looking for is a runtime invisible attribute // use Retention(RetentionPolicy.RUNTIME) on the annotation to make it // visible at runtime AnnotationsAttribute attinfo = (AnnotationsAttribute) minfo.getattribute(annotationsattribute.invisibletag); if (attinfo!= null) { // this is the type name meaning use dots instead of slashes return attinfo.getannotation("com.example.qcon.mains.importantlog"); return null;

80 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); if (annotation!= null) { List<String> parameterindexes = getparamindexes(annotation); currentmethod.insertbefore(createjavastring( currentmethod, classname, parameterindexes)); return cclass.tobytecode(); return null;

81 lets code private List<String> getparamindexes(annotation annotation) { ArrayMemberValue fields = (ArrayMemberValue) annotation.getmembervalue( fields ); if (fields!= null) { MemberValue[] values = (MemberValue[]) fields.getvalue(); List<String> parameterindexes = new ArrayList<String>(); for (MemberValue val : values) { parameterindexes.add(((stringmembervalue) val).getvalue()); return parameterindexes; return Collections.emptyList();

82 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); if (annotation!= null) { List<String> parameterindexes = getparamindexes(annotation); currentmethod.insertbefore(createjavastring( currentmethod, classname, parameterindexes)); return cclass.tobytecode(); return null;

83 lets code private String createjavastring(ctmethod currentmethod, String classname, List<String> indexparameters) { StringBuilder sb = new StringBuilder(); sb.append("{stringbuilder sb = new StringBuilder"); sb.append("(\"a call was made to method '\");"); sb.append("sb.append(\""); sb.append(currentmethod.getname()); sb.append("\");sb.append(\"' on class '\");"); sb.append("sb.append(\""); sb.append(classname); sb.append("\");sb.append(\"'.\");"); sb.append("sb.append(\"\\n Important params:\");");...

84 lets code private String createjavastring(ctmethod currentmethod, String classname, List<String> indexparameters) { StringBuilder sb = new StringBuilder(); sb.append("{stringbuilder sb = new StringBuilder"); sb.append("(\"a call was made to method '\");"); sb.append("sb.append(\""); sb.append(currentmethod.getname()); sb.append("\");sb.append(\"' on class '\");"); sb.append("sb.append(\""); sb.append(classname); sb.append("\");sb.append(\"'.\");"); sb.append("sb.append(\"\\n Important params:\");");... Put multiple statements inside brackets {

85 lets code private String createjavastring(ctmethod currentmethod, String classname, List<String> indexparameters) {... for (String index : indexparameters) { try { int localvar = Integer.parseInt(index) + 1; sb.append("sb.append(\"\\n Index: \");"); sb.append("sb.append(\""); sb.append(index); sb.append("\");sb.append(\" value: \");"); sb.append("sb.append($" + localvar + ");"); catch (NumberFormatException e) { e.printstacktrace(); sb.append("system.out.println(sb.tostring());"); return sb.tostring();

86 lets code private String createjavastring(ctmethod currentmethod, String classname, List<String> indexparameters) {... for (String index : indexparameters) { try { int localvar = Integer.parseInt(index) + 1; sb.append("sb.append(\"\\n Index: \");"); sb.append("sb.append(\""); sb.append(index); sb.append("\");sb.append(\" value: \");"); sb.append("sb.append($" + localvar + ");"); catch (NumberFormatException e) { e.printstacktrace(); sb.append("system.out.println(sb.tostring());"); return sb.tostring(); $0, $1, $2,... can be used to access this and the actual method parameters

87 lets code public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] cfbuffer) throws IllegalClassFormatException { pool.insertclasspath(new ByteArrayClassPath(className, classfilebuffer)); CtClass cclass = pool.get(classname.replaceall("/", ".")); if (!cclass.isfrozen()) { for (CtMethod currentmethod : cclass.getdeclaredmethods()) { Annotation annotation = getannotation(currentmethod); if (annotation!= null) { List<String> parameterindexes = getparamindexes(annotation); currentmethod.insertbefore(createjavastring( currentmethod, classname, parameterindexes)); return cclass.tobytecode(); return null;

88 Javassist Positives Simplicity Do not have to write actual bytecode Decent documentation Negatives Generally slower than ASM Less functionality

89 ASM Released in Open Source in 2002 Actively updated Version released May 2014 Two ASM libraries Event based (SAX like) Visitor design pattern Object based (DOM like) Documentation: asm/asm4-guide.pdf

90 ASM Source:

91 ASM Source:

92 ASM Source:

93 ASM ClassReader: given a byte[], parses a compiled class ClassReader: event producer ClassVisitor: event filter ClassWriter: event consumer BankTrans

94 ASM ClassReader: given a byte[], parses a compiled class ClassReader: event producer ClassVisitor: event filter ClassWriter: event consumer BankTrans visitfield visitmethod

95 ASM ClassReader: given a byte[], parses a compiled class ClassVisitor: delegates class events, event filter visitattribute visitfield visitmethod visitinnerclass visitend ClassReader: event producer ClassVisitor: event filter ClassWriter: event consumer BankTrans visitfield visitmethod

96 ASM ClassReader: given a byte[], parses a compiled class ClassVisitor: delegates class events, event filter visitattribute visitfield visitmethod visitinnerclass visitend ClassWriter: produces output byte[] ClassReader: event producer ClassVisitor: event filter ClassWriter: event consumer BankTrans visitfield BankTrans visitmethod

97 lets code package com.example.qcon.agent; import java.lang.instrument.instrumentation; public class Agent { public static void premain(string agentargs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addtransformer(new ImportantLogClassTransformer());

98 lets code package com.example.qcon.agent; import java.lang.instrument.instrumentation; public class Agent { public static void premain(string agentargs, Instrumentation inst) { System.out.println("Starting the agent"); inst.addtransformer(new ImportantLogClassTransformer());

99 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { //TODO return null;

100 lets code package com.example.qcon.agent; import java.lang.instrument.classfiletransformer; import java.lang.instrument.illegalclassformatexception; public class ImportantLogClassTransformer implements ClassFileTransformer { public byte[] transform(classloader loader, String classname, Class classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { //TODO return null;

101 lets code public byte[] transform(classloader loader, String classname, Class<?> classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_FRAMES); cr.accept(cw, 0); return cw.tobytearray();

102 lets code public byte[] transform(classloader loader, String classname, Class<?> classbeingredefined, ProtectionDomain protectiondomain, byte[] classfilebuffer) throws IllegalClassFormatException { ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_FRAMES); ClassVisitor cv = new LogMethodClassVisitor(cw, classname); cr.accept(cv, 0); return cw.tobytearray();

103 ASM ClassReader: given a byte[], parses a compiled class ClassVisitor: delegates class events, event filter visitattribute visitfield visitmethod visitinnerclass visitend ClassWriter: produces output byte[] BankTrans ClassReader: event producer LogMethod ClassVisitor: event filter visitmethod ClassWriter: event consumer BankTrans

104 ASM Source:

105 lets code public class LogMethodClassVisitor extends ClassVisitor { private String classname; public LogMethodIfAnnotationVisitor(ClassVisitor cv, String pclassname) { super(opcodes.asm5, cv); classname = public MethodVisitor visitmethod(int access, String name, String desc, String signature, String[] exceptions) { // put our logic in here

106 lets code public class LogMethodClassVisitor extends ClassVisitor { private String classname; public LogMethodIfAnnotationVisitor(ClassVisitor cv, String pclassname) { super(opcodes.asm5, cv); classname = public MethodVisitor visitmethod(int access, String name, String desc, String signature, String[] exceptions) { // put our logic in here

107 ASM Source:

108 ASM Source:

109 ASM Source:

110 ASM MethodVisitor: method event filter visitannotation visitend visitcode visittrycatchblock MethodVisitor MethodVisitor login method visitor visitattribute visitcode login method visitor visitend

111 ASM Source:

112 lets code public class LogMethodClassVisitor extends ClassVisitor { private String classname; public LogMethodIfAnnotationVisitor(ClassVisitor cv, String pclassname) { super(opcodes.asm5, cv); classname = public MethodVisitor visitmethod(int access, String name, String desc, String signature, String[] exceptions) { MethodVisitor mv = super.visitmethod(access, name, desc, signature, exceptions); return new PrintMessageMethodVisitor(mv, name, classname);

113 lets code public class PrintMessageMethodVisitor extends MethodVisitor { private String methodname; private String classname; private boolean isannotationpresent; private List<String> parameterindexes; public PrintMessageMethodVisitor(MethodVisitor mv, String methodname, String classname) public AnnotationVisitor visitannotation(string desc, boolean visible) public void visitcode() {

114 lets code public class PrintMessageMethodVisitor extends MethodVisitor { private String methodname; private String classname; private boolean isannotationpresent; private List<String> parameterindexes; public PrintMessageMethodVisitor(MethodVisitor mv, String methodname, String classname) { // initialize instance public AnnotationVisitor visitannotation(string desc, boolean visible) { 1. check method for 2. if annotation present, then get important method param public void visitcode() { 3. if annotation present, add logging to beginning of the method

115 lets code public AnnotationVisitor visitannotation(string desc, boolean visible) { if ("Lcom/example/qcon/mains/ImportantLog;".equals(desc)) { isannotationpresent = true; return new AnnotationVisitor(Opcodes.ASM5, super.visitannotation(desc, visible)) { public AnnotationVisitor visitarray(string name) { if ( fields.equals(name)) { return new AnnotationVisitor(Opcodes.ASM5, super.visitarray(name)) { public void visit(string name, Object value) { parameterindexes.add((string) value); super.visit(name, value); ; else { return super.visitarray(name); ; return super.visitannotation(desc, visible);

116 lets code public class PrintMessageMethodVisitor extends MethodVisitor { private String methodname; private String classname; private boolean isannotationpresent; private List<String> parameterindexes; public PrintMessageMethodVisitor(MethodVisitor mv, String methodname, String classname) { // initialize instance public AnnotationVisitor visitannotation(string desc, boolean visible) { 1. check method for 2. if annotation present, then get important method param public void visitcode() { 3. if annotation present, add logging statement to beginning of the method

117 lets code public void visitcode() { if (isannotationpresent) { // create string builder mv.visitfieldinsn(opcodes.getstatic, "java/lang/system", "out", "Ljava/io/PrintStream;"); mv.visittypeinsn(opcodes.new, "java/lang/stringbuilder"); mv.visitinsn(opcodes.dup);... // add everything to the string builder mv.visitldcinsn("a call was made to method \""); mv.visitmethodinsn(opcodes.invokespecial, "java/lang/stringbuilder", "<init>", "(Ljava/lang/String;)V", false); mv.visitldcinsn(methodname); mv.visitmethodinsn(opcodes.invokevirtual, "java/lang/stringbuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

118 What is Java bytecode? use javap to examine the bytecode

119 What is Java bytecode? public class PrintMessage { private String methodname; private String classname; public PrintMessage(String mname, String cname) { methodname = mname; classname = cname; public void print() { StringBuilder sb = new StringBuilder(); sb.append("a call was made to method \""); sb.append(methodname); sb.append("\" on class \""); sb.append(classname); sb.append("\"."); System.out.println(sb.toString());

120 What is Java bytecode? javap -c bin/com/example/qcon/mains/printmessage

121 What is Java bytecode? javap -c bin/com/example/qcon/mains/printmessage public void print(); Code: 0: new #38 // class java/lang/stringbuilder 3: dup 4: invokespecial #40 // Method java/lang/ StringBuilder."<init>":()V 7: astore_1 8: aload_1 9: ldc #41 // String A call was made to method \" 11: invokevirtual #43 // Method java/lang/ StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder; 14: pop 15: aload_1 16: aload_0 17: getfield #14 // Field methodname:ljava/lang/string; 20: invokevirtual #43 // Method java/lang/ StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;...

122 What is Java bytecode? each line represents one JVM instruction public void print(); Code: 0: new #38 // class java/lang/stringbuilder 3: dup 4: invokespecial #40 // Method java/lang/ StringBuilder."<init>":()V 7: astore_1 8: aload_1 9: ldc #41 // String A call was made to method \" 11: invokevirtual #43 // Method java/lang/ StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder; 14: pop 15: aload_1 16: aload_0 17: getfield #14 // Field methodname:ljava/lang/string; 20: invokevirtual #43 // Method java/lang/ StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;...

123 What is Java bytecode? JVM instruction = 1 opcode with 0 or more operands public void print(); Code: 0: new #38 // class java/lang/stringbuilder 3: dup 4: invokespecial #40 // Method java/lang/ StringBuilder."<init>":()V 7: astore_1 8: aload_1 9: ldc #41 // String A call was made to method \" 11: invokevirtual #43 // Method java/lang/ StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder; 14: pop 15: aload_1 16: aload_0 17: getfield #14 // Field methodname:ljava/lang/string; 20: invokevirtual #43 // Method java/lang/ StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;...

124 What is Java bytecode? Opcode load store lcd return invokevirtual invokespecial Description load a reference onto the stack from a local variable iload, lload, fload, dload, aload stores a value from the stack into a local variable istore, lstore, fstore, dstore, astore push a constant from a constant pool onto the stack method return instruction ireturn, lreturn, freturn, dreturn, areturn, return invoke an instance method on an object invokes an instance method requiring special handling such as an initialization method See the spec for more info:

125 What is Java bytecode? Opcode invokestatic athrow new newarray if<cond> dup Description invoke a class (static) method on a named class throws an exception create a new class create a new array branch if int comparison with 0 succeeds ifeq, ifne, iflt, ifge, ifgt, ifle duplicate the top operand stack value See the spec for more info:

126 What is Java bytecode?

127 What is Java bytecode?

128 What is Java bytecode?

129 lets code public void visitcode() { if (isannotationpresent) { // create string builder mv.visitfieldinsn(opcodes.getstatic, "java/lang/system", "out", "Ljava/io/PrintStream;"); mv.visittypeinsn(opcodes.new, "java/lang/stringbuilder"); mv.visitinsn(opcodes.dup);... // add everything to the string builder mv.visitldcinsn("a call was made to method \""); mv.visitmethodinsn(opcodes.invokespecial, "java/lang/stringbuilder", "<init>", "(Ljava/lang/String;)V", false); mv.visitldcinsn(methodname); mv.visitmethodinsn(opcodes.invokevirtual, "java/lang/stringbuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

130 ASM Positives Speed and Size Decent documentation Depth of Functionality Number of people using framework Negatives Need to write actual byte code longer developer ramp-up

131 Why learn about Java bytecode manipulation frameworks? program analysis find bugs in code examine code complexity generate classes proxies remove access to certain APIs compiler for another language like Scala transform classes without Java source code profilers optimization and obfuscation additional logging

132 Bytecode Manipulation Frameworks ASM: BCEL: CGLib: Javassist: Serp: Cojen: Soot:

133 Make bytecode manipulation frameworks your friend. They might save your job one day. Source:

134

135 Questions? Source: